Ceramic Filtration Mode
Ceramic membrane elements run in cross-flow filtration mode: feed liquid flows parallel to filter surface, and the flow though membrane is performed not so much by pressure drop in membrane, as by particles colloidal movement and turbulent flow movement.
Figure 1. illustrates cross-flow filtration mode.
|Figure 1. Cross-flow filtration through ceramic membrane
In the process of filtration feed liquid flows through channels of ceramic membrane: particles with diameter smaller than pore diameter pass through membrane due to colloidal movement and flow turbulence forming clarified liquid which is permeate.
The particles with diameter bigger than pore size are washed away from membrane surface by liquid flow and form concentrate.
For proper cross-flow filtration it is important to maintain constant flow. That is why an additional amount of feed liquid which corresponds to the amount of permeate obtained is added to the next filtration batch.
Cross-flow filtration features a high filtration speed and a high filtration unit capacity. However, it requires multiply circulation of process liquid through ceramic membrane elements.
Another feature of cross-flow filtration is gradual capacity loss of membrane elements caused by pore contamination by concentrate particles. In order to recover filtration capacity of ceramic element, one should use flushing. Ceramic membrane flushing is performed at increased speed of washing liquid moving through ceramic element channels, which provides washing concentrate particles out of pores and their removal from ceramic element channel. It is possible to use back flushing, either chemical cleaning or CIP, when required.